1. Field of the Invention
The present invention relates to an illumination device for illuminating an original, and an image reading apparatus using the device as illumination means.
2. Related Background Art
An image reading apparatus comprises illumination means for illuminating a film original such as a negative film, reversal film, elongated film, or the like, convey means for conveying the film original, image reading means for reading an image on the film original by receiving light transmitted through the film original, and outputting an image signal, and image processing means for performing arithmetic processing of data of the image read by the image reading means. The image reading apparatus is used for capturing an image on a film original into a so-called personal computer or the like.
A color image is normally read by switching three colors, i.e., red (R), green (R), and blue (B). When small dust particles, scratches, and the like are present on the film original, they appear as black dots (in case of a positive film) or white dots (in case of a negative film) on the read image, thus deteriorating the image quality.
In order to solve such problem, a technique for detecting dust, scratches, and the like on a film original using the feature of infrared rays has been proposed (for example, Japanese Patent Laid-Open Application No. 63-116551). In this case, the image reading apparatus must be capable of reading using infrared rays (IR) in addition to normal reading using three colors, i.e., red (R), green (R), and blue (B).
More specifically, the image reading apparatus which can read using infrared rays (IR) must have light sources that output four color light beams, i.e., red (R), green (R), blue (B), and infrared (IR) light beams.
As is well known, the image reading apparatus must meet compact and low-cost requirements. Even when the apparatus is designed to read using infrared rays (IR), it must be capable of normal reading using three colors.
Hence, an illumination device that can output four color light beams must solve a problem that pertains to the positional relationship upon aligning the beam positions of light beams output from four color light sources in association with a size reduction, in addition to realization of a compact and low-cost arrangement.